Crystallized glass has a thermal expansion coefficient near to that of silicon and also has a low dielectric constant. It has the further advantage that it can be fired at low temperatures. Therefore, it has become of great interest for high density wiring boards for IC packages, multilayers boards, etc. Such boards consist of an insulating substrate comprising the above glass and conductive materials of low resistance metals having low melting points, such as silver, copper, etc. For example, Japanese Patent Application (OPI) No. 12899/80 (the term "OPI" used herein referrs to an unexamined published Japanese Patent Application) proposes a glass ceramic as such. According to this application, a so-called "green sheet" consists of glass particles which crystallize at temperatures lower than the melting point of copper. The green sheet is patterned on its surface by pattern-printing a conductive paste, is laminated to form a monolithic body, and the laminated body is then fired in a predetermined atmosphere.
The "green sheet" described herein referrs to a low-temperature sintered insulating ceramic material having a low dielectric constant and a thermal expansion coefficient near to that of silicon semiconductor chips. Such a green sheet is the molding disclosed in Japanese Patent Applicant (OPI) No. 92943/84, according to which a base composition contains 57 to 63 wt% SiO.sub.2, 20 to 28 wt% Al.sub.2 O.sub.3, 10 to 18 wt% MgO, and 2 to 6 wt% ZnO, to which is added 0.1 to 5 wt% of a crystalline glass composition of B.sub.2 0.sub.3 and/or P.sub.2 O.sub.5 as the frit. The mixture is molded and fired at low temperatures to give a crystallized glass body.
On the other hand, a copper or a copper oxide base metallizing composition which provides tight sealing of the conductive part is required for the paste forming the conductive patterns on the green sheet.
The above copper oxide base composition, however, is disadvantageous in that volume contraction occurs when CuO is reduced to the conductive Cu during heating in a reducing or an inert atmosphere. On the other hand volume expansion occurs in the copper base composition by oxidation of Cu during degreasing in air. The above changes in volume are liable to generate cracks in ceramics and conductive parts.
In addition to the above contraction, when the through holes were filled with metallizing composition, openings would form due to the difference between the contraction coefficient of the Cu and that of the through hole inside wall, or the openings may generate cracks leading to failure of circuit continuity.
Japanese patent application No. 294459/86 proposes a conductive paste composition comprising 80 wt% or higher (according to the copper component thereof) of copper or copper oxide and 12 wt% or lower of MnO.sub.2 and/or 8 wt% of Ag.sub.2 O. However, the adhesion strength of the copper past on the uppermost of the multilayer board is 0.5 kg/mm.sup.2. Therefore, improvement of the adhesion strength is required.